Some epidemiological studies suggest that residential and occupational exposure to power frequency electromagnetic fields (PFEMF) may be a risk factor for the development of certain neoplasms. This association is often weak, however, and there is no generally accepted mechanism to explain how this might occur. The long term goal of this work is to determine whether or not PFEMF (60 Hz) can affect those signal transduction mechanisms that regulate cellular proliferation and thus increase the likelihood of tumorigenesis. Calcium ions are major components of such regulatory pathways and there are suggestions in the literature that a particular calcium regulatory system, the ~capacitative~ calcium entry mechanism, might be sensitive to EMF. a plausible suggestion for why this might be so, especially in the case of stem cells responsible for maintaining renewal cell populations such as those of epithelial and hematopoietic tissues, is presented. If correct, this model could help explain how EMF might increase the risk of cancers and leukemias. The specific aim of this proposal is to test the first part of this hypothesis, i.e., to determine whether or not sinusoidal PFEMF can modulate the entry of Ca2+ through the capacitative entry system in cells. Studies will be done with Swiss 3T3 and SV40-transformed 3T3 cells, rat osteosarcoma cells (ROS 17/2.8) and normal human fibroblasts. The basic protocol will be to activate this system and determine whether or not 60 Hz EMF can modulate the rate at which Ca2+ flows through this system. Activation of this system will be accomplished by depleting the intracellular calcium store with mitogenic agents or the tumor promoter, thapsigargin. During the course of treatment, cells will be exposed to sinusoidal, 60 Hz EMF in the milliTesla range with induced electric field in the 10 to 30 V/cm range using an air gap reactor system developed in this laboratory. One of the advantages of this system is that it allows for resolution between effects due to magnetic fields and those due to induced electric fields. Cytosolic free calcium levels will be monitored in real time by recording light output from the calcium specific, luminescent, photoprotein, aequorin.